1. Field of the Invention
This invention relates generally to a backrest for a seat and, more particularly, to an adjustment apparatus for a seat support.
2. Related Art
An adjustment means is known from U.S. Pat. No. 4,880,271 in which the support element consists of two parallel longitudinal strips firmly interconnected by means of a plurality of transverse strips. Centrally to the longitudinal strips a further sheet metal strip is fixed at its upper end to the uppermost extreme transverse strip of the support element and is also connected to the cams of an excenter device provided at the lower end of the support element, but not to the subsequent transverse strips. The excenter and thus also the cam is adjustable by way of a worm gear by an operating means comprising a handle, in such a manner that the central sheet metal strip, depending en the direction of rotation, brings about an arching or a flattening (detensioning), as the case may be, of the support element such that the adjustment of the desired degree of arching can be brought about. To the rear of the support element at the upper and lower ends thereof a spring is linked up which draws the two ends of the slightly pre-arched support element towards one another, whereby the adjustment in the sense of an increased arching is supported and thereby facilitated. In this context the spring acts permanently onto the support element, even if no adjustment takes place, and is accordingly independent of the operating means.
In addition, the entire mechanism of the arching means is extremely complicated. Furthermore, which ever degree of arching is set up this is stiff and unyielding, whereby comfort is adversely affected.